Transparent conductive films that are required to exhibit light transmittivity are conventionally made from metal oxides such as indium tin oxide (ITO). Examples of such transparent conductive films include a transparent conductive film disposed on a display surface of a display panel such as a touch panel, and a transparent conductive film of an information input device disposed at a display surface-side of a display panel. However, a transparent conductive film made using a metal oxide has expensive production costs as a result of being formed by sputtering in a vacuum environment and is susceptible to cracking and delamination due to deformation by bending, warping, or the like.
Consequently, transparent conductive films made using metal nanowires are being considered as an alternative to transparent conductive films made using metal oxides. This is because a transparent conductive film made using metal nanowires can be formed by coating or printing and is highly resistant to bending and warping. Moreover, transparent conductive films made using metal nanowires are attracting attention as next generation transparent conductive films that are made without using the rare metal indium (for example, refer to PTL 1 and 2).
However, a transparent conductive film described in PTL 1 may appear red and suffer from loss of transparency.
Furthermore, in a situation in which a transparent conductive film made using metal nanowires is disposed at a display surface-side of a display panel, diffuse reflection of external light by the surfaces of the metal nanowires causes black displayed by the display panel to appear slightly brighter, which may be referred to as a “black floating (black level misadjustment)” phenomenon. The black floating phenomenon is a factor that leads to deterioration in display characteristics due to reduced contrast.
A gold nanotube made using gold (Au) has been proposed with the objective of preventing occurrence of the black floating phenomenon since gold has a lower tendency to diffusely reflect light. A gold nanotube is formed by initially using a silver nanowire having a high tendency to diffusely reflect light as a template and subjecting the silver nanowire to gold plating. Thereafter, the silver nanowire portion used as the template is etched or oxidized to enable conversion to a gold nanotube (for example, refer to PTL 3).
Furthermore, a method for preventing light scattering has been proposed (for example, refer to PTL 2) in which metal nanowires are used in combination with a secondary conductive medium (for example, CNTs (carbon nanotubes), a conductive polymer, or ITO).
However, in the case of the gold nanotube obtained by the former of these methods, not only is the silver nanowire used as a template wasted as a material, but a metal material is also required to perform the gold plating. Therefore, this method suffers from high production costs due to having high material costs and a complicated process.
Furthermore, in the case of the latter of these methods, there may be loss of transparency due to the secondary conductive medium (colorant material), such as CNTs, a conductive polymer, or ITO, being located in openings in a metal nanowire network. In addition, this method suffers from high production costs due to having high material costs and a complicated process.
In order to combat these problems, a transparent conductive film has been proposed that includes metal nanowire bodies and a colored compound (dye) adsorbed onto the metal nanowire bodies (for example, refer to PTL 4 and 5).